exports.shuffle=function (arr) {
    //以下方法效率最高
    if (!Array.prototype.shuffle) {
        Array.prototype.shuffle = function() {
            for(var j, x, i = this.length; i; j = parseInt(Math.random() * i), x = this[--i], this[i] = this[j], this[j] = x);
            return this;
        };
    }
    return arr.shuffle();
}